The present invention relates to a heat-exchanger coil assembly. More particularly, the invention relates to a coil assembly for efficiently exchanging heat between a heat-exchange medium accommodated in the body of a heat exchanger and a heat exchange medium flowing through the coil.
Generally, a heat exchanger is based on a pipe system or a plate system The heat exchanger based on the pipe system is used when pressure resistance is required. There are various types of heat exchangers based on the pipe system, such as those based on a coil system or a multiple tube system. Of these, a heat exchanger based on a coil system is widely used for various purposes because the construction is simple, but because the heat transfer area is smaller as compared to the tank (body) capacity, it is used as a heat exchanger in circumstances requiring a relatively small capacity.
FIG. 16 shows a conventional type of heat exchanger based on the coil system. A heat-exchanger coil 101 wound in a spiral form is provided in a body section 104, and an inlet pipe 102 and an outlet pipe 103 are provided at both edges of the coil 101. A heat-exchange medium such as a liquid or a gas is introduced through the inlet pipe 102 passes through the heat-exchanger coil 101, and is discharged through the outlet pipe 103 from the body section 104. Mainly while flowing through the coil 101, heat exchange is executed through the coil wall between the heat-exchange medium in the coil 101 and that in the body section 104.
In order to increase the quantity of exchanged heat and enhance the heat-exchanging capability in the heat exchanger based on the coil system as described above, it is necessary to make the heat transfer area larger by increasing the number of turns in the coil 101. However, in this case, due to friction resistance, the loss of head of the tube becomes greater, and it is required to use a larger capacity pump to keep the flow rate at a specified level.
On the other hand, with the means shown in FIG. 18, it is possible to increase the quantity of heat exchanged. Namely, a header 105 in the heat-exchange medium inlet side and a header 106 in the heat-exchange medium outlet side are provided, and a plurality of inlet pipes 102 as well as outlet pipes 103 for the heat-exchanger coils 101 are connected respectively to the headers 105 and 106. In this case, however, as clearly understood from the figure, capacity of the body section becomes larger, and the efficiency is not always good. Also, the space required for installation of the heat exchanger becomes inevitably larger.
FIG. 19 is a cross-sectional view illustrating a U-shaped multiple tube heat exchanger. The U-shaped type of heat exchanger comprises a plurality of U-shaped tubes 109 each having a different length respectively in order to fit within the body section 107. Each of the U-shaped tubes 109 is supported within the body section 107 by means of a support metal 110 with edge sections in the inlet and outlet sides fixed on a header fixing plate 108.
One heat-exchange medium flows into the body section 107 from an entrance 111 and flows out from an exit 112. The other heat-exchange medium flows into a header space 114 in the inlet side from an entrance 113, flows through the plurality of U-shaped tubes 109 into a header space 115 in the outlet side, and flows out from the exit 116. The heat exchange takes place as the one medium flows through the U-shaped tubes 109 and transfers heat to the medium in the body section 107.
The U-shaped tube heat exchanger described above provides a large heat transfer area, so it is used as a heat exchanger where a large capacity or a large-scale performance is required, as, for instance, in atomic power generating facilities or the like.
However, in this heat exchanger, because the length of each U-shaped tube 109 is different, the loss of head due to tube friction resistance in each U-shaped tube 109 varies from tube to tube. For this reason, the flow velocity or flow rate of heat-exchange medium flowing in each U-shaped tube 109, cannot be kept at a constant level. As a result, thermal stress generated in each U-shaped tube 109 becomes not uniform, and distortion or cracking easily occurs.
Further, the U-shaped tube 109 has a straight portion and a bending section. Any significant distortion difference between the two sections will often cause breakage.
Finally, the supporting forces at the edge sections of the U-shaped tube 109 where the tubes are fixed on the header fixing plate 108 are different from those in the bending section. Thus, when vibration of the tube occurs, fatigue and cracking can take place, especially at the contact section between the U-shaped tube and the support metal 110.